Vertical abrasive belt type surface grinder

ABSTRACT

A metal grinding machine of the endless abrasive belt type in which a power driven contact drum forms the abrasive belt into a downwardly facing narrow work performing band with which the workpiece is engaged by horizontal advance of a reciprocating table onto which the workpiece is secured. The table is slidably mounted on a vertically adjustable bed and is advanced and retracted by a double acting hydraulic cylinder at a controlled rate that remains constant throughout the interval the advancing workpiece is in contact with the abrasive belt. The abrasive belt travels in the same direction the workpiece is advanced so that the swarf resulting from the grinding action is thrown into the rear of the machine where it impinges a curtain of water that issues from a header in the rear of the machine. A second water header located in front of the abrasive belt, provides the option of wet or dry grinding.

United States Patent Elm et a1.

VERTICAL ABRASIVE BELT TYPE SURFACE GRINDER lnventors: Donald C. Elm, St. Paul; Allan J.

Stinn, Minnetonka, both of Minn.

Assignee: Timesavers, Inc., Minneapolis,

Minn.

Filed: Oct. 2, 1974 Appl. No.: 511,352

Primary ExaminerOthell M. Simpson [5 7 ABSTRACT A metal grinding machine of the endless abrasive belt type in which a power driven Contact drum forms the abrasive belt into a downwardly facing narrow work performing band with which the workpiece is engaged by horizontal advance of a reciprocating table onto which the workpiece is secured. The table is slidably mounted on a vertically adjustable bed and is advanced and retracted by a double acting hydraulic cylinder at a controlled rate that remains constant throughout the interval the advancing workpiece is in contact with the abrasive belt. The abrasive belt trav els in the same direction the workpiece is advanced so that the swarf resulting from the grinding action is thrown into the rear of the machine where it impinges a curtain of water that issues from a header in the rear of the machine. A second water header located in front of the abrasive belt, provides the option of wet or dry grindingv 9 Claims, 8 Drawing Figures PATENTEDJUL 8 915 3. 893 265' SHEEI 2 WAT E R PATENTED JUL 8 ms SHEET UUUE V503 PATEMTEnJuL 8 m5 3, 93,255 sum 6 F'IG.7.

F |G.8. 73 23 WORK mace 3'5 42 /Z7 I k A 1 VERTICAL ABRASIVE BELT TYPE SURFACE GRINDER This invention relates to the abrasive machining art and. more particularly, to a metal grinding machine that can be considered a simplified version of the machine of the Grivna et al U.S. Pat. No. 3,8l6,998, which issued June 18, 1974, to the assignee of this invention.

One of the objects of this invention is the provision of a metal grinding machine that utilizes the high speed grinding technique of the Freerks Pat. No. 3,668,814 in a manner that effects substantial savings in the production cost of the machine.

Another object of the invention is to provide a surface grinder in which the workpiece to be ground is fed into and out of engagement with a rapidly traveling endless abrasive belt by placing the workpiece on and securing it to a horizontal reciprocating table.

A significant and highly advantageous feature of the invention resides in the act that the portion of the endless abrasive belt in contact with the workpiece travels in the direction the reciprocating table advances the workpiece into the machine. As a result, there is no danger that the workpiece will be thrown out of the machine if perchance its securement to the table should fail.

Another advantage of having the abrasive belt travel in this direction is that the swarf resulting from the grinding action is thrown into the rear of the machine and not onto the loading and unloading station at the front of the machine.

Since the swarf leaving the zone of action is extremely hot. the invention provides a water curtain in position to be impinged by the swarf.

With a view toward minimizing air pollution resulting from the dust caused by the grinding operation, the invention has as another of its objects the provision of means for drawing the dust-laden air from the machine interior, washing the dust therefrom by passing it through curtains of water, and then filtering solid particles from the water,

Still another object of this invention is to provide a simplified endless abrasive belt type metal grinder that is equally effective for wet and dry grinding, and quickly and easily converted from one to the other mode by simply opening or closing a water valve.

Finally, as with the machine of U.S. Pat. No. 3,816,998, this invention incorporates feed rate control by which the rate of advance of the workpiece while it is being ground by the abrasive belt, is maintained constant at a selected value.

With these observations and objectives in mind, the manner in which the invention achieves its purpose will be appreciated from the following description and the accompanying drawings, which exemplify the invention, it being understood that changes may be made in the specific apparatus disclosed herein without departing from the essentials of the invention set forth in the appended claims.

The accompanying drawings illustrate one complete example of the embodiment of the invention constructed according to the best mode so far devised for the practical application of the principles thereof, and modified embodiments of two parts of the machine, and in which:

FIG. I is a perspective view of the overall machine, taken from the front and left side thereof;

FIG. 2 is a perspective view of the machine viewing the same from the rear and left side;

FIG, 3 is a front view of the machine with parts broken away to better illustrate details of the structure;

FIG. 4 is a vertical sectional view through FIG. 3 on the plane of the line 4-4;

FIG. 5 is a horizontal sectional view through FIG. 3 on the plane of the line 5-5,

FIG. 6 diagrammatically illustrates the hydraulic cir cuitry by which the double acting cylinder that advances and retracts the reciprocating work carrying table is controllably connected with a fluid pressure source;

FIG. 7 illustrates a modification of the abrading head of the machine; and

FIG. 8 more or less diagrammatically illustrates a modification of the work carrying table,

Referring to the accompanying drawings in which like reference characters designate like parts through out the several views, the numeral 10 designates generally the main frame ofa surface grinder embodying this invention. This frame is a rigid weldment and has a base section 11 with right and left side sections l4 and I5 rising therefrom and connected at the top to define a generally rectangular space above the base section. In the upper part of this space, there is located an abrading head generally designated by the numeral 16. This abrading head is essentially like that of the Bernu Pat. No. 3,777,442, issued Dec. ll, I973, to the assignee of this invention, and hence comprises an endless abrasive belt l7 trained around an upper tensioning roll 18 and a lower contact drum [9 to travel in a vertically oriented oval shaped orbit, the axes of which are horizontal.

The contact drum is journalled in coaxial bearings that are mounted in brackets 20-20 which are fixed to and depend form the underside of a horizontal arm 21, which in the art is known as the center bar of the abrading head. This center bar is solidly secured to the right side section 14 of the main frame and extends, cantilever fashion, towards the left side section of the machine to which it is separably connected in the manner disclosed in tha aforesaid Bernu patent.

The upper tensioning roll 18 is journalled in bearings mounted in the arms of a yoke 22 which is supported from the center bar by the ram of an air cylinder 23, solidly mounted in the center bar. An increase in pressure in the air cylinder thus tensions the abrasive belt and a reduction in pressure allows the roll 18 to lower to permit removal and replacement of the belt.

An electric motor 24 drivingly connected with the contact drum l9 through a belt-type transmission 25 drives the abrasive belt at high speed around its vertically oriented oval orbit, and although the contact drum may have a diameter in excess of l2 inches, the bottommost portion of that orbit theoretically is a line parallel to the axis of the contact drum. It is along that line that the abrasive belt engages a workpiece being ground, but since the machine is capable of removing stock to a substantial depth in one pass of the workpiece, the zone of contact between the abrasive belt and the workpiece is more accurately defined as a narrow band that is concave in cross section.

The contact drum can be regarded as a backup member, since it supports the abrasive band against the thrust of the work thereon. For rapid stock removal it is preferable to use a contact drum as the backup memher, but for finish grinding a pressure shoe 19' shown in FIG. 7, does a better job. In each case the backup member gives the bottommost part of the abrasive belt that engages the workpiece its cross sectional shape the difference between the two being in the width of its work performing band. Where the backup member is in the form of a pressure shoe, it is flanked by a pair of rolls 26-26, the former being power driven.

workpieces to be ground are fed against the work performing band of the abrasive belt by a reciprocating table 27 that is slidably mounted on a bed member 28 in the form of a rigid horizontal frame.

Although the slidable mounting of the table on the bed member may be provided by conventional scraped ways, it is far less costly to do this with a pair of parallel guide shafts 29 extending fore and aft of the bed memher, and bearings 30 on the underside of the table in which the guide shafts 29 are slidably received.

The table is slid along the guide shafts 29 to and from a loading and unloading station in front of the machine by feed means which may be in the form ofa lead screw and nut reacting between the bed member 28 and the table 27, but which in the illustrated embodiment of the invention is a double acting cylinder 31. The closed end of this cylinder is securely connected. as at 32, to a cross bar 33 which forms the rear of the rigid frame that constitutes the bed member, and the rod 34 of the cylinder is connected by means of a clevis and pin 35 to the underside of the front portion of the table. Pressure in the rod end of the cylinder thus advances the table from a position at the loading and unloading station of the machine to carry a workpiece thereon into work performing engagement with the abrasive belt, and pressure in the closed end of the cylinder effects retraction of the table. At the loading and unloading station, the workpieces are placed on and secured to the table with the surface thereof which is to be ground facing upward and horizontal, and after being ground are removed from the table.

Obviously, the elevation of the table with respect to the work performing band of the abrasive belt at the bottommost part of its orbit, will determine the depth to which the top surface of the workpiece is ground off as the advancing table carries it into engagement with the abrasive belt. That elevational relationship must be adjustable, not only to accommodate workpieces of different thicknesses but also to enable the depth of cut to be regulated and chosen for optimum results, bearing in mind that different metals will require different depth settings. This needed adjustability is obtained by mounting the rigid frame that constitutes the bed member 28 or four jack screws 36 that are located at the corners of the base section of the main frame.

The nuts 37 in which the jack screws 36 are threaded are freely rotatably (but not axially movably) confined in cages 38 that are fixed to the base section of the main frame. Hence, upon simultaneous rotation of the nuts, the bed member and all structure thereon may be raised or lowered as needed to obtain the desired elevational relationship between the workpiece surface to be ground and the work performing band of the abrasive belt. Such simultaneous rotation is imparted to the nuts 37 by turning a handwheel 39 on the left side of the machine, and drivingly connected with the nuts through a conventional sprocket and chain transmission, part of which is indicated at 40 in FIG. 3.

Since the nuts of all four jack screws rotate simultaneously and at the same rate during adjustment of the elevation ofthe bed member, the bed member rises and falls with a translatory motion and, to guide that motion. the opposite side sections 14 and i5 of the main frame have vertical track forming plates 41 fixed thereto and projecting inwardly towards the adjacent side rails 42 of the bed frame to be slidably received in gibbed ways 43 fixed to these side rails.

An important feature of this invention resides in the fact that at the bottom of its orbit, the abrasive belt travels in the same direction the workpieces are advanced into the machine in other words, towards the rear of the machine. This is contrary to conventional practice; but, as a result of this departure from the cus' tomary directional relationship between belt travel and infeed of work, two very significant advantages are achieved in abrasive grinding of metai. Both of these concern the safety of the machine operator.

With the abrasive belt traveliing in the conventional direction, there is a very real danger that a workpiece will be forcefully ejected from the front of the machine where the operator is stationed. since there is no assurance that the securement of the workpiece to the table will never fail. Moreover, if the abrasive belt travels in the conventional direction. the swarf which results from the grinding operation whether the grinding takes place during the advance of the workpiece into the machine or its retraction from the machine is thrown towards the front of the machine, which cannot be closed since there must be an entrance through which the workpieces enter the machine.

By contrast, with the abrasive belt traveling in the direction the workpieces are advanced, if perchance the securement of a workpiece does fail, the loose workpiece will not be thrown out of the front of the machine but rather into its closed rear portion. While such an accident could result in some damage to the machine. the far more serious possibility of injury to the operator would be spared.

The rearwardly projected swarf resulting from the grinding impinges upon a falling curtain of water 44 and is carried thereby into a drain pan 45 located in the lower portion of the main frame beneath the bed 28. The water curtain 44 issues from a header 44 that ex tends horizontally across the lower rear portion 47 of the enclosure 48 for the abrading head.

A drain opening 49 in the lower part of the pan 45 allows the water to flow therefrom into a collecting trough 50 at the rear of the machine. Preferably the trough is equipped with a slowly moving filter belt 51 that extends across its top to remove solids from the water draining into the trough.

To effectively close the rear of the machine, the rear wall 47 of the enclosure for the abrading head, coacts with a hood 52 that sets on the adjacent portion of the drain pan 45 and accommodates the rear portion of the bed member 28 and the table reciprocating cylinder 31.

Dust laden air is drawn out of the machine enclosure by an exhaust fan 53 (diagrammatically illustrated in FIG. 2) mounted at the top of the enclosure and discharging into a duct 54. The output end of this duct is positioned to discharge onto the filter belt 51, and to water down the airborne dust, water is projected into the upper part of the duct through a supply line 55, to

cascade off of a series of baffles 56 that are mounted at different levels in the duct.

A second water header S7 is located in the enclosure for the abrading head in front of the downwardly traveling stretch of the abrasive belt with its discharge ports positioned to project the streams issuing therefrom onto the abrasive belt. A valve (not shown) controls the flow of water to this second header, so that by simply opening this valve the machine is converted from a dry grinding mode to a wet grinding mode, it being understood that, for some materials, wet grinding is preferable to dry grinding, and vice versa.

As explained hereinbefore, by raising or lowering the bed member 28 by means of the hand wheel 39, the machine can be adjusted to differently dimensioned workpieces. By this same adjustment, the amount or depth of stock to be ground off of the workpiece may be selected For each of the different materials amenable to abrasive machining there is an optimum depth of cut, but that can be quickly and easily selected by reference to an experience chart or left to the expertise of the operator. In any event, once the correct depth-ofcut setting has been made for a given workpiece, all like workpieces will be ground to the same dimension by advance and retraction of the table.

In the normal operation of the machine the work piece surface will be ground to the selected dimension during the advance of the table so that little or no work is done during retraction of the table. Nevertheless, the abrasive belt will be in contact with the just ground surface to improve its finish, and any swarf that results from that finishing action, like that produced by the initial grinding action, will be projected against the falling curtain of water 44.

lffor some reason it is found desirable to operate the machine in such manner that during advance or infeed of the table little or no grinding takes place and all or practically all of the grinding is done during the outfeed of the table, the aforesaid advantages of having the abrasive belt travel in the described direction will be realized to the same extent as they are in the normal operation of the machine.

Those skilled in the art will understand that the abrasive belt travels at a very high rate of speed on the order of five thousand feet (5,000 ft.) per minute, which of course is many times greater than the rate at which the workpiece is advanced. By virtue of this significantly large differential in speed between belt travel and advance of the workpiece, the force with which the cylinder 3] advances the table and the workpiece thereon, is augmented by the tendency of the abrasive belt traveling in the same direction as the workpiece to pull the workpiece into the machine. In any event, the resulting horizontally directed force has a component that reacts vertically between the backup member for the abrasive belt and the bed member and produces the feed force or pressure that exists between the abrasive belt and the workpiece.

As in the aforesaid Grivna et al. U.S. Pat. No. 3816998, the rate at which the workpiece is fed against the abrasive belt is controlled and maintained constant during the abrading action; despite discontinuities in the surface being ground. The manner in which this control is effected is diagrammatically illustrated in FIG. 6 which illustrates the hydraulic circuitry by which the double acting cylinder is actuated. As there shown, the opposite ends of the cylinder 3! are alternatively and selectively connected with a hydraulic pressure line 60 and a drain line 61. The source of the hydraulic pressure has not been illustrated since it can take any one of several different conventional forms.

Conventional solenoid actuated selector valves 62 and 63 determine which end of the cylinder is connected with the pressure source. Energization of the solenoid of valve 62 affects connection of the rod end 64 of the cylinder with the pressure source and connection of its closed end with the drain line; while energization of the solenoid of valve 63 effects reversal of those connections and connects the closed end 65 of the cylinder with the pressure source.

The electrical circuits by which these solenoids are energized are not shown, since they are conventional, but it should be understood that the energization of the solenoid of valve 63 to effect retraction of the table by pressurizing the closed end of the cylinder, is effected by closure of a switch in response to completion of the advancing stroke of the table, and that when the table reaches the loading and unloading station that switch is opened.

Energization of the solenoid of valve 62 to effect advance of the table can be initiated by manual closure of a switch (not shown) or automatic closure thereof if the machine is arranged to operate in an automatic mode.

Feed rate control, both during the advance and the retraction of the table is accomplished by interposing unidirectional flow control valves 66 and 67, respectively, in the lines leading to the rod end and to the closed end of the cylinder. These flow control valves have bypasses 66' and 67' around them, and solenoid actuated selector valves 68 and 69 determine whether the flow control valve or its bypass is connected in the circuit.

Considering first the situation that obtains during retraction of the table, brought about by connection of the closed end of the cylinder with the pressure line 60 (which resulted from energization of the solenoid of selector valve 63), during that portion of the retraction stroke in which the workpiece is in contact with the abrasive belt, the flow control valve 66 is in the circuit to maintain a selected constant rate of table retraction. But the instant the workpiece leaves contact with the abrasive belt, a switch (not shown) is closed by an actuator 70 that is adjustably connected with the table and moves with it. That closure effects energization of the solenoid of valve 68 with the result that the hydraulic fluid flowing out of the closed end of the cylinder bypasses the flow control valve 66 so that the remainder of the retraction stroke of the table is at a faster rate.

In like manner, the flow control valve 67 and its bypass 67, along with their associated selector valve 69, govern the rate at which the table advances. In this case, though, it is the initial portion of the stroke that takes place at the fast rate and, for that purpose. the solenoid of the valve 69 is energized and remains so until just before the table has advanced far enough to bring the workpiece thereon into engagement with the abrasive belt. At that instant, the switch controlling energization of the solenoid of valve 69 is opened by an actuator 71 adjustably connected with the table, with the result that the flow control valve 67 takes over and controls the feed rate of the table.

It is important to note that by controlling flow out of the cylinder, the flow control valve 67 resists the force advancing the table and thereby maintains control of its rate of advance. despite the fact that this force results in part from the tendency of the abrasive belt to pull the workpiece into the machine.

The manner in which workpieces are secured to the table can take any of a number of different forms and will depend largely upon the geometry ofthe part to be machined. As an example. it may be done by clamping bolts the heads of which are received in T slots 72 formed in the surface of the table; or by an electromagnetic chuck secured to the table.

It is also possible to mount a rotary work holder on the table. as diagrammatically indicated in FIG. 8. As there shown, a turret 73 is rotatably mounted on the table to be driven by a hydraulic motor (not shown) in the manner illustrated and described in the Grivna et al US. Pat. No. 3,Sl6.998. Any suitable way of securing the workpiece to the turret can be employed. If the turret is mounted at a fixed elevation with respect to the table, the feed force with which the rotating workpiece is fed against the abrasive belt results from the horizontal advance of the table in the manner described.

On the other hand, it is also possible if desired to mount the turret 73 on an arm hinged to the table. as in the Grivna et al patent, and to produce the feed force by hydraulic cylinders that react vertically between the table and the hinged arm. In this case, advance of the table would merely bring the turret under the abrading head.

While in the foregoing description of the preferred embodiment of the invention the workpiece is ground to the desired dimension during the advance or infeed of the work carrying table and finished during the retraction or outfeed of the table. the advantages of the invention are also realized if during the infeed of the table the workpiece makes no contact at all with the abrasive belt and all grinding is done during the retraction of the table. Obviously, of course. in this case there would have to be an upward adjustment of the bed before retraction of the table began. By the same token the invention also lends itself to embodiment in a machine in wh ch significant grinding takes place during both the at" rance and retraction of the table.

Those skilled in the art will appreciate that the invention can be embodied in forms other than as herein disclosed for purposes of illustration.

The invention is defined by the following claims:

1. A metal grinding machine having a work loading station. the machine being of the type wherein the grinding is done by a. an abrading head having an endless abrasive belt mounted to travel in a vertically oriented noncircular orbit, the parallel axes of which are substantially horizontal,

b. power drive means to impart orbital travel to the abrasive belt. and

c. a backup member extending transversely across and inside the orbit of the belt at the bottom of the orbit to form the bottommost part of the belt into a work performing band that extends straight across the width of the belt, and wherein during the grinding operation the workpiece is supported with its surface to be ground substantially horizontal, facing upward and engaging said work performing band of the abrasive belt, said machine being characterized by:

A. work supporting means below the abrading head comprising 1. a bed member defining a path that leads from the loading station of the machine and is transverse to said work performing band.

2. a table to support a workpiece and present the surface thereof which is to be ground to the abrasive belt.

3. means slidably mounting the table on the bed member in a manner which transmits all downward loads on the table directly to the bed member said members (i.e. the backup member and the bed member) being adjustably movable vertically relative to one another to enable the machine to accommodate differently dimensioned workpieces;

B. means to effect said adjustment and thereby establish the elevation of the table at a level at which the surface of the workpiece to be ground is at a level above that of said work performing band of the abrasive belt;

C. feed means arranged to react between the bed member and the table to advance and retract the table along said path and thereby feed the workpiece against the work performing band of the abrasive belt with a force that has a component reacting vertically between said backup member and the bed member as the travel of the table presents unground portions of the workpiece surface to the abrasive belt; and

D. control means operatively connected with said feed means to resist the same and thereby govern the rate at which said feed means feeds the workpiece against the abrasive belt and maintain said rate constant during the grinding action, notwithstanding discontinuity in the workpiece surface being ground.

2. The machine of claim 1, further characterized in that the abrasive belt is driven in the direction to cause it to traverse the workpiece surface in the direction tending to draw the table into the machine and away from its work loading station, so that the swarf that results from the grinding action during either the advance or the retraction of the table is thrown to the rear of the machine away from its loading station.

3. The machine of claim 2, further characterized by means for producing and maintaining a curtain of water in the rear of the machine in position to be impinged by the swarf resulting from the grinding action.

4. The machine of claim 3, further characterized by an enclosure for the abrading head, suction means arranged to draw dust-laden air from the enclosure,

duct means into which said suction means discharges the dust-laden air,

means to introduce water into said duct means in a manner to cause it to collect the dust entering the duct means, and

a reservoir to receive the discharge from said duct means as well as the water forming said swarfcollecting curtain.

5. The machine of claim 4, further characterized by filter means across the top of the reservoir to intercept solids that are suspended in the water issuing from said duct means and in the water forming the swarf-collecting curtain.

6. The machine of claim 2, further characterized by a water header in front of the abrading head to project water onto the abrasive belt for wet grinda se ond water header behind the abrading head to form a curtain of water in position to be impinged by the swarf that results from the grinding action. and

control means for regulating and governing flow of water to said headers, whereby the machine is quickly adaptable to either dry or wet grinding.

7. The machine of claim 1, further characterized in that said feed means comprises a double acting hydraulic cylinder, and duct means through which the opposite ends of said cylinder are selectively and alter natively connectable with a fluid pressure source and with a reservoir to effect advance and retraction of the table, and wherein said adjustable control means (element D of claim 1) comprises a flow control valve arranged to meter flow out of the cylinder during advance of the table. 8. The machine of claim 7, further characterized by solenoid actuated control valve means connected in said duct means to control connection of the opposite ends of the cylinder with fluid pressure source and with the reservoir and thereby determine the direction of table travel, and a control switch operatively connected with the solenoid of said control valve means and arranged to be actuated by motion of the table to automatically effect a change in the direction of table travel from advance to retraction. 9. The machine of claim 8, further characterized by means including a solenoid actuated control valve providing a bypass around said flow control valve, and a control switch for the solenoid of said control valve arranged to be actuated by motion of the table to effect energization of the solenoid of said control valve and closure ofsaid bypass when the table has advanced a predetermined distance. whereby further advance of the table is at the rate determined by said flow control valve (recited in claim 7). 

1. A metal grinding machine having a work loading station, the machine being of the type wherein the grinding is done by a. an abrading head having an endless abrasive belt mounted to travel in a vertically oriented non-circular orbit, the parallel axes of which are substantially horizontal, b. power drive means to impart orbital travel to the abrasive belt, and c. a backup member extending transversely across and inside the orbit of the belt at the bottom of the orbit to form the bottommost part of the belt into a work performing band that extends straight across the width of the belt, and wherein during the grinding operation the workpiece is supported with its surface to be ground substantially horizontal, facing upward and engaging said work performing band of the abrasive belt, said machine being characterized by: A. work supporting means below the abrading head comprising
 1. a bed member defining a path that leads from the loading station of the machine and is transverse to said work performing band,
 2. a table to support a workpiece and present the surface thereof which is to be ground to the abrasive belt,
 3. means slidably mounting the table on the bed member in a manner which transmits all downward loads on the table directly to the bed member, said members (i.e. the backup member and the bed member) being adjustably movable vertically relative to one another to enable the machine to accommodate differently dimensioned workpieces; B. means to effect said adjustment and thereby establish the elevation of the table at a level at which the surface of the workpiece to be ground is at a level above that of said work performing band of the abrasive belt; C. feed means arranged to react between the bed member and the table to advance and retract the table along said path and thereby feed the workpiece against the work performing band of the abrasive belt with a force that has a component reacting vertically between said backup member and the bed member as the travel of the table presents unground portions of the workpiece surface to the abrasive belt; and D. control means operatively connected with said feed means to resist the same and thereby govern the rate at which said feed means feeds the workpiece against the abrasive belt and maintain said rate constant during the grinding action, notwithstanding discontinuity in the workpiece surface being ground.
 2. a table to support a workpiece and present the surface thereof which is to be ground to the abrasive belt,
 2. The machine of claim 1, further characterized in that the abrasive belt is driven in the direction to cause it to traverse the workpiece surface in the direction tending to draw the table into the machine and away from its work loading station, so that the swarf that results from the grinding action during either the advance or the retraction of the table is thrown to the rear of the machine away from its loading station.
 3. The machine of claim 2, further characterized by means for producing and maintaining a curtain of water in the rear of the machine in position to be impinged by the swarf resulting from the grinding action.
 3. means slidably mounting the table on the bed member in a manner which transmits all downward loads on the table directly to the bed member, said members (i.e. the backup member and the bed member) being adjustably movable vertically relative to one another to enable the machine to accommodate differently dimensioned workpieces; B. means to effect said adjustment and thereby establish the elevation of the table at a level at which the surface of the workpiece to be ground is at a level above that of said work performing band of the abrasive belt; C. feed means arranged to react between the bed member and the table to advance and retract the table along said path and thereby feed the workpiece against the work performing band of the abrasive belt with a force that has a component reacting vertically between said backup member and the bed member as the travel of the table presents unground portions of the workpiece surface to the abrasive belt; and D. control means operatively connected with said feed means to resist the same and thereby govern the rate at which said feed means feeds the workpiece against the abrasive belt and maintain said rate constant during the grinding action, notwithstanding discontinuity in the workpiece surface being ground.
 4. The machine of claim 3, further characterized by an enclosure for the abrading head, suction means arranged to draw dust-laden air from the enclosure, duct means into which said sUction means discharges the dust-laden air, means to introduce water into said duct means in a manner to cause it to collect the dust entering the duct means, and a reservoir to receive the discharge from said duct means as well as the water forming said swarf-collecting curtain.
 5. The machine of claim 4, further characterized by filter means across the top of the reservoir to intercept solids that are suspended in the water issuing from said duct means and in the water forming the swarf-collecting curtain.
 6. The machine of claim 2, further characterized by a water header in front of the abrading head to project water onto the abrasive belt for wet grinding, a second water header behind the abrading head to form a curtain of water in position to be impinged by the swarf that results from the grinding action, and control means for regulating and governing flow of water to said headers, whereby the machine is quickly adaptable to either dry or wet grinding.
 7. The machine of claim 1, further characterized in that said feed means comprises a double acting hydraulic cylinder, and duct means through which the opposite ends of said cylinder are selectively and alternatively connectable with a fluid pressure source and with a reservoir to effect advance and retraction of the table, and wherein said adjustable control means (element D of claim 1) comprises a flow control valve arranged to meter flow out of the cylinder during advance of the table.
 8. The machine of claim 7, further characterized by solenoid actuated control valve means connected in said duct means to control connection of the opposite ends of the cylinder with fluid pressure source and with the reservoir and thereby determine the direction of table travel, and a control switch operatively connected with the solenoid of said control valve means and arranged to be actuated by motion of the table to automatically effect a change in the direction of table travel from advance to retraction.
 9. The machine of claim 8, further characterized by means including a solenoid actuated control valve providing a bypass around said flow control valve, and a control switch for the solenoid of said control valve arranged to be actuated by motion of the table to effect energization of the solenoid of said control valve and closure of said bypass when the table has advanced a predetermined distance, whereby further advance of the table is at the rate determined by said flow control valve (recited in claim 7). 